From the news page of Loudness, and also various FB pages on the topic.

LOUDNESS Apologizes For U.S. Tour Cancelation: 'We Plan To Learn From This Experience'. Japanese metallers LOUDNESS have released a statement and apology to fans for the cancellation of the band's previously announced U.S. tour.

The trek was scrapped after the band was denied entry to the United States Tuesday night at a Chicago airport, apparently due to the new immigration policies from the Trump administration. The news of the tour's cancellation was broken by the Chicago club Reggies, where LOUDNESS was scheduled to perform Wednesday night. LOUDNESS wrote on its official web site: 'We greatly regret to inform you that, due to various reasons, the planned tour scheduled for the U.S. has been postponed, effective immediately.

'LOUDNESS deeply apologizes for any inconvenience that this may cause our fans. We plan to learn from this experience, prepare more accordingly, and we promise to put on a U.S. tour again in the near future. Please wait a little while longer until that is possible.'

LOUDNESS's record company confirmed to The Asahi Shimbun that the four members of the band had been refused entry at the airport on April 18.
'In previous tours, we were able to enter through the hosts' invitation, but this time it didn't work,' said a record company official. The record company's comments echo those made by LOUDNESS's agency Katana Music, which told Japan Today that the band was able to enter the United States in the past with proper invitation letters but that the immigration this time requested visas for the musicians. Reggies owner Robby Glick told the Chicago Tribune that he spoke to the band's publicist who cited an issue with 'exemption papers,' which were acceptable for entry the last time the band visited the U.S., but denied this time around. 'It's a little bit harder,' said Glick. 'I don't know if it's a product of the administration or if LOUDNESS was flying by the seat of their pants, but there is a difference since our new president came in.'

Sounds to me as if they were always 'flying by the seat of their pants' previously. Speaking as a journalist, things were toughened up in the early 90s with regards being able to go on tour with bands or even simply interview them to cover them for UK publications and you had to have a visa or you were denied entry, so if you were working in the US as a band you would most certainly have had to have proper documentation. No different from the UK, as one or two musicians have discovered in recent years.

Looks like they did not fill out the appropriate paperwork. I'm off to the States in a couple of weeks myself and have had to fill in an ESTA, which is what Japanese citizens also have to do it they want to travel there. http://www.esta.u.......silly boys.